The World Health Organization has documented almost 100 cases of the H7N9 avian flu virus in the first month of 2014. Chinese state-run media, Xinhua, reports that 19 of those infected have died.

Case numbers from early 2014 already rival those of 2013, in which health experts reported around 149 cases and 46 deaths total.

Poultry markets continue to be a source of infection in 2014, said virologist Hualan Chen of the Harbin Veterinary Research Institute in China. In a January 28 presentation at the ASM Biodefense and Emerging Diseases Research Meeting in Washington, D.C., Chen called on Chinese officials to close the markets, which act as mixing bowls for influenza viruses.

Chen also presented data suggesting that H7N9 viruses are mutating to become better at causing disease in humans and mammals.